Transfer to and from vessels and fixed structures at sea, or on other large bodies of water, such as larger lakes, is inherently dangerous in particular because of the relative movement between the vessels or between the vessel and the fixed structure. Often, personnel are required to transfer to and from a relatively small vessel, which is subject to movement by waves, wind and tide from and to a vertical ladder of a larger vessel or fixed structure. In the circumstances it is all too easy for untrained or inexperienced personnel to slip or trip and find themselves in the water, where they risk serious injury or drowning. Transfer between larger vessels and vessels of comparable size is no less dangerous. For these reasons, safety regulations limit the transfer of personnel at sea to relatively calm conditions, typically where the maximum wave height is less than 0.7 m. It follows that considerable amounts of working time can be lost due to bad weather conditions, which adds considerable expense to companies operating in the marine environment.